Compositions involving V2 O3 -Al2 O3 -CaO

ABSTRACT

The present invention pertains to novel phases involving V 2  O 3 , Al 2  O 3  and CaO, and the method for their preparation. The solid compositions involving V 2  O 3 , Al 2  O 3 , and composition diagram of V 2  O 3  -Al 2  O 3  -CaO as shown in the drawing herein e.g., FIG. 1. The composition may be used as a catalyst for oxidation or reduction reactions.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to compositions involving V₂ O₃ -Al₂ O₃ -CaO.

SUMMARY OF THE INVENTION

The present invention pertains to novel solid compositions involving V₂O₃ -Al₂ O₃ -CaO and the method for their preparation. The solidcompositions involving V₂ O₃ -Al₂ O₃ -CaO fall within a polygon in aternary composition diagram of V₂ O₃ -Al₂ O₃ -CaO as described in thedrawing herein e.g. FIG. 1. The polygon has the vertices andcorresponding coordinates in weight percent as shown in Table I.

                  TABLE I                                                         ______________________________________                                                Coordinates (wt %)                                                    Vertices  V.sub.2 O.sub.3                                                                             Al.sub.2 O.sub.3                                                                      CaO                                           ______________________________________                                        D         37             1      62                                            E         15            23      62                                            F         15            48      37                                            G         51            48       1                                            H         98             1       1                                            ______________________________________                                    

The compositions involving V₂ O₃, Al₂ O₃ and CaO having compositionsfalling within the polygon shaped shaded area in the ternary compositiondiagram of V₂ O₃, Al₂ O₃ and CaO as shown in the FIG. 1 are made by theprocess comprising the steps of:

(1) heating V₂ O₅ powder having a particle size of less than about 50microns in an atmosphere in which the partial pressure of oxygen is inthe range of 10⁻⁶ to 10⁻¹⁰ atmosphere and the CO₂ /H₂ volume ratio is inthe range of about 10/1 to 1/1 while gradually increasing thetemperature stepwise over a temperature range of about 600° C. to 1300°C. and holding the final temperature at about 1300° C. for a period ofat least about 24 hrs. to ensure complete reduction of all vanadium toV^('+) ;

(2) heating Al₂ O₃ powder having a particle size of less than about 50microns for a period of about 10 to 14 hrs. at a temperature in therange of about 1000° C. to 1200° C.;

(3) heating CaCO₃ powder having a particle size of less than about 50microns for a period of about 10 to 14 hours at a temperature in therange of about 600° C. to 1100° C.; whereby, substantially all of saidCaCO₃ is converted into CaO;

(4) thoroughly grinding together about 15 to 98 wt. % of V₂ O₃ from (1)with about 1 to 48 wt.% of Al₂ O₃ from (2) and about 1 to 62 wt. % ofCaO from (3) to produce a mixture having a grain size of less than about50 microns.

(5) pelletizing the mixture from (3) at a pressure of about 5,000 psi;and

(6) heating and reacting together the mixture of pellets from (5) at atemperature in the range of about 700° C. to 1500° C. for a period inthe range of about 12 to 48 hrs. in an atmosphere in which the partialpressure of oxygen is in the range of 10⁻¹⁰ to 10⁻⁶ atmosphere toproduce said solid composition involving V₂ O₃, Al₂ O₃ and CaO.

In one embodiment, the pellets from step (6) are cooled to ambienttemperature while at substantially the same partial pressure of oxygenas in step (6). Preferably, to prevent undue oxidation and moisturepickup, the cooled pellets are stored in a sealed container.

BRIEF DESCRIPTION OF THE DRAWING

The drawing e.g. FIG. 1 depicts a ternary composition diagram showing apolygon shaped shaded area circumscribed by DEFGH within which usefulcompositions involving V₂ O₃, Al₂ O₃ and CaO are found.

DESCRIPTION OF THE INVENTION

The subject newly synthesized solid compositions involving V₂ O₃, Al₂ O₃and CaO and mixtures thereof are depicted in FIG. 1. This work has ledto synthesizing new phases in which vanadium in several oxidation statesare accommodated such as to render crystalline phases thermodynamicallystable over a wide range of oxygen pressures at elevated temperatures.

The newly synthesized solid compositions involving V₂ O₃, Al₂ O₃ and CaOare shown as falling within the polygon shaped shaded area in theternary composition diagram in the FIG. 1. The oxidation states ofvanadium in the substitutional solid compositions vary in the range of+3 to +5. The polygon shaded area DEFGH has the following vertices andcorresponding coordinates in weight percent:

    ______________________________________                                                Coordinates (wt %)                                                    Vertices  V.sub.2 O.sub.3                                                                             Al.sub.2 O.sub.3                                                                      CaO                                           ______________________________________                                        D         37             1      62                                            E         15            23      62                                            F         15            48      37                                            G         51            48       1                                            H         98             1       1                                            ______________________________________                                    

Three stable intermediate phases designated C₅, C₉, and CaVO₃ aredepicted in FIG. 1. C₅ is used herein to designate a complex calciumvanadate of the general formula Ca₅ V₃ O_(x), where X=9.5-12.5. C₉ isused herein to designate a complex calcium vanadate of the generalformula Ca₉ V₆ O_(x), where x=18-24.

A first newly synthesized material comprises a solid solution of V₂ O₃with Al₂ O₃, wherein the Al₂ O₃ is present in admixture with said V₂ O₃in the amount of about 1-20 wt.% (basis wt. of mixture). Included insaid solid solution are mixtures of CaVO₃ and Al₂ O₃, wherein the Al₂ O₃is present in the amount of about 5.0 to 45.0 wt.% (basis wt. ofmixture). These compositions exist within that portion of the area ofcomposition triangle CaVO₃ -Al₂ O₃ -V₂ O₃ that falls within polygonDEFGH, as shown in FIG. 1, wherein said portion of common area is apolygon circumscribed by PQGH. This composition is illustrated by pointK in FIG. 1 having the following coordinates in wt.%: V₂ O₃ 70, Al₂ O₃15 and CaO 15. The onset of partial melting in this composition is inthe range of about 1025° C. to 1075° C.

A second newly synthesized material comprises the phases CaVO₃, C₉ andAl₂ O₃. These compositions exist within that portion of the area ofcomposition triangle C₉ -Al₂ O₃ -CaVO₃ that falls within polygon DEFGH.As shown in FIG. 1 said common area is a polygon circumscribed by RSQP.This composition is illustrated by point L in FIG. I having the (7following coordinates in wt.%. V₂ O₃ 45, Al₂ O₃ 15 and CaO 40. The onsetof partial melting of this composition is in the range of about 1035° C.to 1085° C.

A third newly synthesized material comprises the C₉, CaO.6Al₂ O₃, andAl₂ O₃. These compositions exist within that portion of the area ofcomposition triangle C₉ -CaAl₁₂ O₁₉ - Al₂ O₃ that falls within polygonDEFGH. As shown in FIG. 1, this common area is a polygon circumscribedby TUSR. This composition is illustrated by point M in FIG. I having thefollowing coordinates in wt.%: V₂ O₃ 30, Al₂ O₃ 35, and CaO 35. Theonset of partial melting in this composition is about 1425° C. to 1475°C.

The subject compositions made from V₂ O₃, Al₂ O₃ and CaO are synthesizedin the following manner. The identity of the reaction product, stablesolid phases involving V₂ O₃, Al₂ O₃ and CaO may be confirmed by X-raydiffraction analysis.

First, V₂ O₃ is prepared by heating commercially availableanalytical-grade V₂ O₅ having a particle size of less than about 50microns in a vertical tube furnace in an atmosphere of carefullyselected oxygen pressure within the stability range of V₂ O₃ e.g. in therange of 10⁻⁶ to 10⁻¹⁰ atmospheres. This is accomplished by using a gasmixture of high-purity CO₂ and H₂ in controlled proportions. The CO₂ /H₂ratio by volume is in the range of 10/1 to 1/1. The relatively lowmelting point of the starting vanadium oxide (V₂ O₅), e.g. about 690°C., necessitates heating the oxide slowly. Starting at a temperature ofabout 600° C., the temperature is gradually increased stepwise over aperiod of about 12 to 24 hrs. to a final temperature of about 1300° C.At that temperature the oxide is held at least about 24 hrs. e.g. 24 to30 hrs to ensure complete reduction of all vanadium to V³⁺.

Preheated analytical-grade oxides having a particle size of less thanabout 50 microns are used as starting materials for the other componentsof the stable solid phases to be synthesized. The CaCO₃ is heated forabout 10 to 14 hrs at a temperature in the range of about 600° C. to1100° C. prior to being used in preparation of the final materials. Bythis means, substantially all, e.g. more than 95 wt.% of the CaCO₃ isconverted in CaO. Al₂ O₃ is separately heated for about 10 to 14 hrs ata temperature in the range of about 1000° C. to 1200° C. prior to beingused in preparation of the final mixtures.

The mixtures of the three oxide components are mechanically groundtogether under acetone in an agate mortar to ensure thorough mixing anda sufficiently small grain size e.g. less than 50 microns. For example,about 15 to 98 wt.% of V₂ O₃ is ground together with about 1 to 62 wt.%of CaO and about 1 to 48 wt.% of Al₂ O₃ to produce a mixture having agrain size of less than about 50 microns. Complete formation of thedesired compounds in the succeeding heat treatment is thereby promoted.Next, the oxide mixtures are pelletized at a pressure of about 5,000 psior higher. The pellets may have any conventional size e.g. 1/16"to 1".The pellet mixture is then heated at a temperature in the range of about700° C. to 1500° C., such as about 700° C. to 1050° C. or about 1050° C.to 1500° C. for a period in the range of about 12 to 48 hrs. (dependingon the nature and solidus temperature of the phase to be synthesized) ina vertical tube furnace with carefully controlled oxygen pressures, inthe range of 10⁻¹⁰ to 10⁻⁶ atmosphere. In the manner describedpreviously for preparing V₂ O₃, the pellets are heated in a furnaceatmosphere provided by a gas mixture of CO₂ and H₂ in various desiredmixing ratios, typically in the range of about 10/1 to 1/1. Theseselected ratios are kept constant for the duration of the synthesis byuse of a differential manometer. By this method the oxygen pressure atthe specified temperature can be controlled to better than ±1%. Thethermodynamic data for the water-gas reaction (CO₂ +H₂ =CO+H₂ O), onwhich the calculations were based, are known with extremely highaccuracy (better than 0.1%), and hence the method used ensures reliableaccurate control of the oxidation state of vanadium during thesynthesis. This is extremely important for optimization of theproperties of the finished product.

At the time of the high temperature reaction, all of the oxide pelletsmay be in the solid state or at least one, two or three of the oxideconstituents may be in the molten state. At the reaction conditionsprevailing in the subject process, solid solutions may be made bysolid-state reactions considerably below temperatures at which a liquidphase is present. However, the presence of a liquid phase or asolid-liquid phase improves the kinetics of the reaction.

The individual oxide components were heated to a sufficiently hightemperature to expel absorbed or adsorbed water. Well defined startingmaterials for accurately weighing up mixtures are thereby produced. Aspreviously described, V₂ O₅ was heated slowly to a temperature of about1300° C. at controlled oxygen pressures in order to decompose the V₂ O₅slowly to V₂ O₃. By this means, violent reactions are avoided at thehighest temperatures, and the vanadium is produced in the desiredoxidation state V³⁺.

The oxide mixtures were heated at temperatures in the range of about700° C. to 1500° C. in order to promote reaction among the oxidecomponents to the desired finished products consisting mainly of one ormore (solid-solution) phases. In one embodiment, the mixture of solidparticles was heated to a temperature below the solidus, for example toabout 1000° C. The phase assemblage of the final product was producedentirely by solid state reaction. Under such conditions, the reactionproducts were relatively small, typically, of about 0.1to 5.0 microns.In another embodiment, the mixtures were heated to a sufficiently hightemperature e.g. about 1500° C. to produce partial or complete melting.This speeds up the reaction and produces reaction products of largersize, typically in the range of about 2-75 microns. After heating themixtures at this high temperature for a period of time, such as 12-48hrs, the composition is cooled to ambient conditions. For example, thecomposition may be cooled slowly (over a period of 1/2-1 hr) to about1200° C. From this temperature, the composition may be cooled rapidly(quenched) to room temperature. During these runs the oxygen pressure ofthe gas phase was controlled by using gas mixtures of CO₂ and H₂, CO₂and CO, or H₂ O/H₂ in the range of about 10/1 -1/1. These selectedratios are kept constant for the duration of the synthesis, for example,by use of a differential manometer.

The new solid compositions that have been synthesized by the subjectinvention at relatively reducing conditions imposed by a CO₂ -H₂atmosphere with a CO₂ /H₂ volume ratio that provides a controlledpartial pressure of oxygen in the range of about 10⁻⁶ -10⁻¹⁰ have stableoxidation states that vary in the range of about +3 to +5.

The pellets of the composition involving V₂ O₃ -Al₂ O₃ -CaO may be usedas an oxidation or reduction catalyst in the conventional catalyticoxidation or reduction of a reactant material such as an organicmaterial or an oxygen containing gas. They offer improved activity andyields and greater stability over a wider temperature range e.g. about900° C. or higher than that which is offered by typical oxidationcatalysts. For example, as an oxidation catalyst the subject pellets maybe used in the conversion of o-xylene to phthalic anhydride, butene tomaleic anhydride, or alcohols to aldehydes or organic acids. As areduction catalyst, the pellets may be used to reduce the oxide ofnitrogen to nitrogen.

As previously noted, the newly identified solid compositions involvingV₂ O₃ -Al₂ O₃ -CaO contain vanadium in many different oxidation states.This is important for the oxidation-reduction catalysts described above.Further the CaO may moderate the acidity and make these materialsselective oxidation- reduction catalysts. In addition, they are stablesolids at relatively high temperatures.

Various modifications of the invention as herein before set forth may bemade without departing from the spirit and scope thereof, and therefore,only such limitations should be made as are indicated in the appendedclaims.

We claim:
 1. A composition produced from V₂ O₃, Al₂ O₃ and CaO whereinsaid composition falls within polygon DEFGH as shown in the disclosedFIG.; wherein the amounts of V₂ O₃, Al₂ O₃ and CaO are characterized asshown in the table below;

    ______________________________________                                                Coordinates (wt %)                                                    Vertices  V.sub.2 O.sub.3                                                                             Al.sub.2 O.sub.3                                                                      CaO                                           ______________________________________                                        D         37             1      62                                            E         15            23      62                                            F         15            48      37                                            G         51            48       1                                            H         98             1       
 1.                                          ______________________________________                                    


2. A composition as provided in claim 1 and as illustrated by point K insaid disclosed FIG., wherein said composition has the followingcoordinates in wt.%: V₂ O₃ 70, Al₂ O₃ 15, and CaO
 15. 3. A compositionas provided in claim wherein said composition exists within PQGH.
 4. Acomposition as provided in claim 1 and as illustrated by point L in saiddisclosed Figure, wherein said composition has the following coordinatesin wt.%: V₂ O₃ 45, Al₂ O₃ 15 and CaO
 40. 5. A composition as provided inclaim 1, wherein said composition exists within polygon RSQP.
 6. Acomposition as provided in claim 1, and as illustrated by point M insaid disclosed Figure, wherein said composition has the followingcoordinates in wt.% V₂ O₃ 30, Al₂ O₃ 35 and CaO
 35. 7. A composition asprovided in claim 1 wherein said composition exists within polygon TUSR.8. A composition as provided in claim 1 wherein said composition is asolid solution.
 9. A method of preparing a composition from V₂ O₃, Al₂O₃ and CaO wherein said composition falls within the polygon DEFGH asshown in the disclosed Figure, and wherein said method comprises thesteps of:(1) heating V₂ O₅ powder having a particle size of less thanabout 50 microns in an atmosphere in which the partial pressure ofoxygen is in the range of 10⁻⁶ to 10⁻¹⁰ atmospheres while starting at atemperature of about 600° C. and gradually increasing the temperatureover a period in the range of about 12 to 24 hours to about 1300° C. andholding the temperature at about 1300° C. for a period to ensurecomplete reduction of all vanadium to V³⁺ ; (2) heating Al₂ O₃ powderhaving a particle size of less than about 50 microns for a period ofabout 10 to 14 hrs at a temperature in the range of about 1000° C. to1200° C.; (3) heating CaCO₃ powder having a particle size of less thanabout 50 microns for a period of about 10 to 14 hrs at a temperature inthe range of about 600° C. to 1100° C., whereby substantially all ofsaid CaCO₃ is converted into CaO; (4) thoroughly grinding together about15 to 98 wt.% of V₂ O₃ from (1), with about 1 to 48 wt.% of Al₂ O₃ from(2), and about 1 to 62 wt.% of CaO from (3) to produce a mixture havinga grain size of less than about 50 microns; (5) pelletizing the mixturefrom (4) at a pressure of about 5000 psi; and (6) heating and reactingtogether the mixture of pellets from (5) at a temperature in the rangeof about 700° C. to 1500° C. for a period in the range of about 12 to 48hrs in an atmosphere in which the partial pressure of oxygen is in therange of 10⁻¹⁰ to 10⁻⁶ atmosphere.
 10. The method of claim 9 whereinsaid Figure the amounts of V₂ O₃, Al₂ O₃ and CaO are characterized asshown in the Table below;

    ______________________________________                                                Coordinates (wt %)                                                    Vertices  V.sub.2 O.sub.3                                                                             Al.sub.2 O.sub.3                                                                      CaO                                           ______________________________________                                        D         37             1      62                                            E         15            23      62                                            F         15            48      37                                            G         51            48       1                                            H         98             1       
 1.                                          ______________________________________                                    


11. The method of claim 9 provided with the steps of cooling the pelletsfrom ( 6) to ambient temperature, while at substantially the samepartial pressure of oxygen as in (6); and storing the cooled pellets ina sealed container.
 12. The method of claim 9 wherein said compositionis a solid solution.
 13. The method of claim 9 where in step (6) saidpellets are heated in an atmosphere involving a gas mixture of CO₂ andH₂ with a volume ratio of CO₂ /H₂ in the range of about 10/1 to 1/1. 14.The method of claim 9 where in steps (1) and (6) said materials areheated in an atmosphere involving a gas mixture of CO₂ and CO or H₂ Oand H₂ in volumetric ratios CO₂ /CO or H₂ O/H₂ in the range of about10/1 to 1/1.
 15. The method of claim 9 wherein said composition isillustrated by point K in said disclosed Figure wherein said compositionhas the following coordinates in wt. %: V₂ O₃ 70, Al₂ O₃ 15 and CaO 15.16. The method of claim 9 wherein said composition is illustrated bypoint L in said disclosed Figure wherein said composition has thefollowing coordinates in wt. %: V₂ O₃ 45, Al₂ O₃ 15 and CaO
 40. 17. Themethod of claim 9 wherein said composition is illustrated by point M insaid disclosed Figure wherein said composition has the followingcoordinates in wt.%: V₂ O₃ 30, Al₂ O₃ 35 and CaO
 35. 18. Compositionproduced from Al₂ O₃, V₂ O₃ and CaO wherein the oxidation state of thevanadium in said composition is in the range of about +3 to +5 andwherein said composition is characterized by its ability to catalyzeoxidation-reduction reactions and said composition falls within thepolygon DEFGH as shown in the disclosed Figure, and wherein the amountsor Al₂ O₃, V₂ O₃ and CaO are characterized as shown in Table I.